code: def _union_names(est, in_names=None):
      return [
          "{}:{}".format(trans_name, feat_name)
          for trans_name, trans, _ in est._iter()
          for feat_name in transform_feature_names(trans, in_names)
      ]
  
file_path: eli5/eli5/sklearn/transform.py
imports: import numpy
  from sklearn.pipeline import Pipeline, FeatureUnion
  from sklearn.feature_selection.base import SelectorMixin
  from sklearn.preprocessing import MinMaxScaler, StandardScaler, MaxAbsScaler, RobustScaler
  from eli5.transform import transform_feature_names
  from eli5.sklearn.utils import get_feature_names
label_desc: Use image node_id 4 for calling a global function with example usage: _union_names(est, in_names) and returns: unknown